Ion implantation is an important process in semiconductor/microelectronic manufacturing. The ion implantation process is used in integrated circuit fabrication to introduce controlled amounts of dopant ions into semiconductor wafers. An ion-source is used to generate a well-defined ion beam for a variety of ion species from a dopant gas. Ionization of the dopant gas generates the ion species which can be subsequently implanted into a given workpiece.
Carbon has emerged as a widely used dopant in the semiconductor industry for a variety of material modification applications such as inhibiting diffusion of co-dopants or enhancing stability of the doped region. In this regard, carbon dioxide (CO2) has emerged as a common dopant source for carbon ion implantation. However, it has been observed that CO2 behaves as an oxidizing gas which tends to oxidize tungsten ion chamber components to form various tungsten oxide (WOx) deposits along electrode surfaces and chamber components of the ion apparatus. The occurrences of such deposits are problematic, as they deteriorate the electrical properties, thereby requiring a higher voltage to sustain a stable plasma. However, higher voltages can result in voltage discharge, which causes electrical shorting and momentary drops in the beam current. The beam current drops are commonly referred to as “beam glitching”. The beam glitching degrades the ion source performance to a degree where the process cannot operate with acceptable efficiency. In such cases, the user may be required to abort the implant operation and perform maintenance or replace the ion source. Such downtime results in productivity loss of the ion implantation system. Hence, it is necessary to maintain proper functioning of the ion source for extended periods of time in order to perform a high quality implant process.
In view of the undesirable deposits associated with CO2 as a dopant source for ion implantation, carbon monoxide (CO) has emerged as an alternative dopant gas source as a result of the lower oxygen content in CO. The lower oxygen content reduces the amount of WOx formation. However, CO has been observed to form heavy carbon (C) and tungsten carbide (WC) deposits during the operation of the ion source. C deposits are a result of plasma decomposition of CO, whereas WC deposits form as a result of the interaction of CO and its plasma fragmented products with tungsten-based chamber components. The C/WC deposits can create beam glitching, thereby creating concerns of short ion source life.
Furthermore, CO is a toxic gas which poses significant safety and environmental challenges. CO is typically stored in cylinders under high pressures. Storage of CO under high pressure is unacceptable because of the possibility of developing a leak or catastrophic rupture of the cylinder. Accordingly, standard high pressure cylinders for CO pose hazards of the unintended release of these fluids from high pressure cylinders.
There is an unmet need to reduce deposits in an ion chamber when utilizing a carbon-based dopant gas source for carbon implantation, along with a method and system for a safe storage and delivery device for carbon-based dopant gas sources. Other aspects of the present invention will become apparent to one of ordinary skill in the art upon review of the specification, drawings and claims appended hereto.